The present invention relates to a cassette holder into which a large cassette and a small cassette are selectively loaded.
A known type of cassette holder allows a large cassette and a small cassette in the same recording format to be selectively loaded.
This type of cassette holder has a cassette opening into which a large cassette fits. Therefore, this type of cassette holder is equipped with a positioning-restriction mechanism for restricting the position of a small cassette so that the small cassette can be accurately loaded into a predetermined position in the holder, through the cassette opening having the large-cassette size.
FIG. 1 is a perspective view showing major components of a known cassette holder having a small-cassette positioning-restriction mechanism.
Illustrated in FIG. 1 are components peripheral to a cassette opening through which a large cassette (not shown) or a small cassette 1S is loaded. The cassette opening has the right size (width and height) for the large cassette.
An upper surface 2a of a frame 2 is a part of the bottom surface of the cassette opening. A shaft 3 is pivotally mounted on the frame 2. Integrally formed on the shaft 3 are guides 4a and 4b, the positioning-restriction mechanism for restricting the position of the small cassette 1S in the cassette holder.
The guides 4a and 4b protrude from the bottom surface of the cassette opening (the upper surface 2a of the frame 2). The distance between the guides 4a and 4b matches the width of the small cassette 1S so that the cassette 1S can be loaded into the cassette holder between the guides 4a and 4b. 
The small cassette 1S comes into contact with either the guide 4a or 4b when it is shifted to left or right while being loaded. The cassette 1S is thus obstructed from being loaded by the guide 4a or 4b. In other words, the cassette 1S cannot be loaded into any position other than a predetermined position. The guide 4a or 4b thus guide the small cassette 1S to the predetermined position.
Although not shown in FIG. 1, the known cassette holder is equipped with a cassette detector for detecting that a large cassette wider than the smaller cassette 1S is loaded. It is provided inside the cassette holder (in a cassette-loading direction) when viewed from the cassette opening. It is located between the guides 4a and 4b, and the front-end section of the cassette opening (in a cassette-unloading direction).
When the cassette detector detects the loaded large cassette, the shaft 3 rotates until the guides 4a and 4b are positioned at the same level as or lower than the bottom surface of the cassette opening.
This mechanism allows the large cassette to be loaded into the cassette holder with no obstruction by the guides 4a and 4b. 
As explained, the large and small cassettes can be selectively loaded into the known cassette holder.
Another component not shown in FIG. 1 is a flap for shutting the cassette opening. The guides 4a and 4b thus cannot be viewed from outside when the cassette opening is shut by the flap.
This mechanism causes users inconveniences such that he or she has to shift the small cassette 1S in left and right to find the guides 4a and 4b when loading it through the cassette opening via the flap.